The present invention relates generally to electric power conversion systems, and more specifically to a high-voltage high-frequency converter with a slip slide power conditioner which removes non-monotonic non-linearities induced by stray capacitances and inductance leakae in transformer windings.
Chopper converter power supplies are useful for converting a D.C input into a new D.C voltage or an A.C. voltage of a desired frequency. This result is achieved by passing the input D.C. voltage through a series of switches simulating an A.C. voltage which is impressed upon the primary of a transformer. The secondary output voltage is dependent upon the ratio of the number of the windings of the primary to the secondary, while the frequency of the output voltage is dependent upon the rate of switching of the input D.C. voltage. Where the chopper is driven by high-frequency switching signals, an equivalent high frequency output can be achieved.
In conventional D.C.-to-D.C. converter systems, the output signals are often subject to contamination by the effects of stray capacitances and inductance leakage in the windings of the transformer. Exemplary converter system are disclosed in the following U.S. Patents, the disclosures of which are incorporated by reference:
U.S. Pat. No. 3,925,715 issued to Venable;
U.S. Pat. No. 4,034,280 issued to Crownin et al;
U.S. Pat. No. 4,187,458 issued to Milberger et al; and
U.S. Pat. No. 4,208,706 issued to Suzuki et al.
All of the above-cited references disclose conditioning circuits which are designed to act as L-C filters and reduce stray inductance and capacitance contamination in the output of converters. Currently, there exists a need to reduce such contamination in high-power applications of Milberger converter systems.
The Milberger converter is best understood by referring to the U.S. patent application Ser. No. 910,113 entitled "The Milberger Converter", filed on Jan. 28, 1986, the disclosure of which is incorporated by reference. The Milberger converter has an advantage over conventional converters in that its output is conditioned by two independent square waves which either add or cancel. The output voltage is directly proportional to a percentage of addition time to the total time, i.e., Vo equals Vp (T.sub.ADD /T.sub.TOTAL).
As disclosed in the above-cited reference, the Milberger converter's 100 percent dynamic range, small size, and reduced number of parts are among its main advantages. However, a problem has been encountered when the Milberger converter is used in high voltage and high power applications. Medium power is, in the present context, defined as electrical power of around 100 watts, and high-power is considered to be electrical power above 10 kw. In high-voltage and high-power applications there exists a non-monotonic increase in the output voltage of the Milberger converter, which occurs when its control circuit commands a linear increase. Investigation of the phenomenon indicates that it is caused by the occurrence of the presence of an ultra-high frequency ripple on top of the pulses of the output waveform. When this ripple is in phase with the output signal, it adds and the output increases. As the phase of the ripple shifts, it alternately increases and decreases on top of the output signal.
The task of reducing these non-monotonic increases in the output signals of Milberger converters in high-power applications is alleviated by the U.S. patent application entitled "Self-Generated Converter Filter" by C. S. Kerfoot et al, the disclosure of which is incorporated by reference. The disclosure of Kerfoot et al describes the design of Milberger converter systems and provides self-generated conditioning to their output signal which has the same effect as an "add-on" filter. The design of the Kerfoot et al reference produces a reduction of non-monotonic degradation characteristics of converter output signals by minimizing the number of secondary windings used in the transformer. More specifically, the transformer is redesigned so that it retains its primary winding; but its secondary windings (being n in number and having a total of N turns) is, in one embodiment, replaced by m replacement secondary windings (where m is an integer less than n). When the replacement secondary windings have a total of N turns they produce an output signal with reduced degradation normally caused by stray capacitance and inductance leakage in the secondary windings.
The Kerfoot et al reference is directed towards the same problem as the present invention. However, it is not always convenient to replace the transformer secondary windings, as proposed by Kerfoot et al. In such instances, there remains a need to provide a power conditioner which reduces the effects of stray capacitances and inductance leakages on the output signal of converters (including the Milberger Converter). The present invention is intended to satisfy that need.